TRADITIONAL AND NEW DESIGNS OF THE HAMMER MILL ROTOR
The essential elements of a typical hammer mill rotor are: pivoting or rigidly attached hammers, a surrounding
screen or screens, and a grinding plate or plates, as well as the supporting structure and drive system. In hammer mills,
material moves from the hopper to the working zone, where the rotor with hammers is installed. The supplied material,
under the impact of the hammers, attains significant speed (40 to 110 m s-1), and the particles move in a circular path, hitting the grinding plates (if installed), the screen, and
each other. Due to the impact forces, the fragmented material remains in the grinding chamber until the particles reach sizes smaller than the holes in the screen. After obtaining the relevant geometric features, the fragmented material moves out of the grinding chamber through the holes in the screen (Flizikowski, 2005; Munson, 2010).
A disadvantage of the traditional design of hammer mills is their low throughput in relation to energy consumption, as described by Bochat and Wesołowski (2009) and Kapur et al. (1990). This is mostly due to the structure of the rotor, which is equipped with hammers that have the shape of rec- tangular plates. As a result, due to the impact of the hammers, the particles move along circular tracks. They form a thin rotating layer on the inner circumference of the grinding chamber, with the result that the material, in spite of a sufficient degree of fragmentation, continues to circulate for a long time before it passes through the screen. Figure 1 shows a traditional hammer mill rotor in isometric view.